Temperature indicating or control apparatus



C 5 1954 J. s. WooDwARD TEMPERATURE INDTCATTNG 0R CONTROL APPARATUSFiled OCT.. l, 194'? 0.- PRE- Mpl/HE IN V EN TOR.

PR-/l/VPZ/HER LSI boda/afa Patented OctD 5, 1954 STATS PATENT OFFICETEMPERATURE INDICATING OR CONTROL APPARATUS 3 Claims.

The present invention is related to temperature responsive indicating orcontrol apparatus, and especially to such apparatus as is concerned withthe measurement of very high temperatures.

In the measurement of very high temperatures, it is customary to use athermocouple, which produces an electrical voltage proportional to thetemperature to which the ther-mocouple is subjected. Such therrnocouplesare very sensitive. However, the thermocouple structures are verydelicate. When a thermocouple is subjected to an oxidizing atmosphere atvery high temperatures, it burns out very quickly. Also, if the `gas inwhich it is immersed carries dust or ne particles of soot, a.depositsoon forms on the thermocouple which adversely affects itscharacteristics. The thermocouple must therefore be protected from thegas in which it is immersed. This may readily be accomplished byproviding a protective casing around .the thermocouple. However, such acasing introduces a lag between temperature changes outside the casingand temperature vchanges inside the casing at the thermocouple. In orderto iind an accurate indication of temperature, .the thermocouple outputmust be compensated for this lag.

This `problem has been found to be particularly troublesome in themeasurement of the temperature on the exhaust gases of a jet engine.Such engines run at very high temperatures which are very close to thelimit which the materials used will withstand. It is therefore desirableto provide some means for measuring the temperature of the gases in theengine and for reducing the supply of fuel to the engine before the:temperature becomes too high, so as to maintain the temperature at asafe value. Since the temperature in the engine may fluctuate rapidly,it is necessary that the temperature measuring device be not onlyaccurate but also immediately responsive to changes in temperature.

It is therefore an object oi the lpresent invention to provide improvedtemperature responsive means for measuring accurately vtemperatureswhich change rapidly.

A further object is .to provide, for use in connection ywith vathermocouple, Aimproved temperature indicating or control meansresponsive V'to both the thermocouple-temperature and the rate ofchan-ge of 4that temperature,

Another object is to provide, in connection with an electricaltemperature measuring device which is used in a protective ca sing,means Vfor compensating the output of the electrical temperavturemeasuring device vfor the lag behind the temperature being measured dueto the protective casing Aaround the device.

Another object .is to provide an improved velectrical system whichresponds both to the magnitude and the rate .of change of a voltageimpressed upon it.

Other objects ,and advantages of the present invention will becomeapparent from a consideration of the appended specification, `claims anddrawing, in which Figure l illustrates, somewhat diagrammatically, afuel supply control system for a jet engine embodying the principles ofmy invention, and

Fig. 2 illustrates, diagrammatically, a modied form of electricalcircuit Which may be used in the system of Fig. l.

Referring to Fig. 1, there is shown at IB a portion of the tail pipe orexliust conduit of a jet engine. Projecting through the wall of theexhaust conduit is an insulator l2 carrying a thermocouple |4. A casing|16 surrounds -the thermocouple 'I4 to protect it from direct contactwith the very hot highly oxidizing gases of the jet engine exhaust.

A pair of conductors I1 and I8 connect lthe thermocouple to the inputterminals of a preamplier 20. The output terminals of the preamplifier20 are connected by conductors 22 and 24 to a series circuit consistingof a resistance 26 and an inductance 2B. A contact 30 is slidablyadjustable .along vresistance 26, and is connected by a conductor 32 toan input terminal of an amplifier 34. An extension of conductor 24connects Wit'h the other input terminal of amplifier 34.

The output terminals of amplifier 34 are connected in one arm of aWheatstone bridge circuit generally indicated at 36 and having a pair ofinput terminals 38 and 43, and a pair of output terminals 42 and 44.

A fixed resistance 46 is connected between input terminal 38 and outputterminal 42. Connected between input terminal 40 and output terminal 442is aibranch consisting of a conductor 43, the

output terminals of amplifier 34, a conductor 41,

a fixed resistance 48, and a conductor 50. Input vterminal 40 isconnected to output terminal 44 lbyineans of conductors 60 and 62 to apolarized relay A(i4. The relay 64 includes a contact 66 movablevbetween,stationary contacts/.58 and 1.0. The

relay 64 controls a reversible motor generally indicated at 12, havingan armature 'I4 and field windings 'i6 `and 18.

When contact 66 engages contact 68, an energizing circuit is completedior armature '|4 and field winding 18. This circuit may be traced fromthe upper terminal of the secondary winding 80 of a transformer 82through a conductor 84, contacts, 66 and 68, a conductor 86, fieldwinding 18, conductors 88 and 5U, and armature 'F4 to the lower terminalof winding 8D.

When contact 66 engages contact l0, an energizing circuit for armature'I4 and field winding T6 is completed, which may be traced from theupper terminal of winding 80 through conductor 84, contacts 66 and ill,conductor 92, eld winding 16, conductors S4 and 9|), and armature 'i4 tothe lower terminal of winding 80.

The motor 'E2 drives a shaft 96, which carries an internally threadednut 98, A threaded shaft tot rides in the nut 68, and is suitably guidedto prevent its rotation. The shaft |00 carries the slider ri'he oppositeend of shaft lili! serves a valve to control the flow of uid from an yinlet conduit |62 to a conduit |04 leading to a chamber |56. One side ofchamber |66 is closed by diaphragm |68. The chamber 66 is provided withan outlet passage H0 having a restriction H2 therein. The diaphragm lScarries at its center a valve H4, which controls the 3 flow of i'uelfrom an inlet passage I6 to an outlet passage i I8.

Operation It is weil known that the rate of flow of heat "Men two pointsat different temperatures is rtional to the difference between thosetem- C otures. Hence thc rate of ow of heat from .jet engine exhaustgases to the thermocouple Eli is proportional to the diference betweenthe temperature and the thermocouple temperature. It has been found thatthe temperature of the gas is equal at any time to the thermocoupletemperature lplus a constant factor times the rate of change of thethermocouple temperature. In order to measure the gas temperature,therefore, it is necessary to add a component which varies with thethermocouple temperature to a component which varies with the rate ofchange of the thermocouple temperature. The sum of two such components,if they are properly s ected to compensate for the lag of thethermocouple behind the changes in the gas temperature, will give a trueindication of the gas ternpcraturo at any instant.

The output potential of the thermocouple I4 measure oi' the temperatureat the thermo- This potential is by the pre-amplier 26, and the amedpoten'ial is then impressed across the re- 2E and inductance 2S inseries.

itial drop across resistance 26 varies ce with the steady state valueo1" the Under constant tial drop across inductance is zero, but n thethermocouple temperature and its outootcntial vary, the potential dropacross ince '2B varies in accordance with the rate oi change or" thethermocouple output potential.

he oniplier 3d amplifier, potential which is the s ol? the drop acrossinductance 2S plus e n on of the drop across resistance E6. Theproportion of the total drop across resistance 26 which is used as apart of the input potential ampiiiier 34 may be varied by moving theslider 313 along resistance 26. The slider 36 should be so adjusted thatthe same ratio exists between the portion of the potential drop acrossresistance 'Zt which is utilized in the amplier 34 and the temperatureat thermocouple i4, and between the potential drop across inductance 28and the change in the rate of flow of heat from the exhaust gases to thethermocouple i4. If the slider 36 is properly set in that manner, thenthe input potential to ampiier is a measure of the temperature of theexhaust gases.

This input potential is amplified by the ampliicr 3!! and is thenimpressed in one arm of the Wheatstone bridge circuit 36. Any unbalanceof the bridge circuit causes the polarized relay ed to operate thereversible motor 'I2 to drive shaft Q6 in the proper direction so thatslider 53 moves along resistance 56 to restore the balance of the bridgecircuit. Any unbalance of the bridge circuit is caused by a change inthe te" perature of the exhaust gases, and since such un. lalance causesa rebalancing of the bridge circuit by a movement of slider 5S, it maybe stated that the position of slider 58 along resistance 56 is ameasure of the temperature of the exhaust ce It may also be stated thatthe lateral i .sinon of shaft |66 is a measure of the temperature of theexhaust gases. If desired, a suitable indicator Si may be attached tothe shaft |00 to indicate on a suitable scale EGE the exhaust gastemperature.

When the exhaust gas temperature exceeds a predetermined value, theright end of shaft |00 moves to the left so as to open the port leadingto conduit |62', thereby permitting fluid to flow from inlet conduit E62to conduit |94 and thence to chamber E66. Since the chamber |66 has arestricted outlet, the pressure in chamber |06 will build up as soon asthe inlet valve is Opened by an amount greater than the restriction H2.When that happens, the chamber |56 expands, clos the valve H4 andshutting' o or reducing the supply of fuel to the engine until safetemperature conditions are again restored.

ahen the valve at the end oi shaft |66 is closed, the fuel inletpressure acting on the underside of diaphragm |08, forces valve illlopen, so as to permit a flow of fuel to the engine.

Figure 2 '.ihcre is shown in Fig. 2 a modified electrical circuit, inwhich elements which correspond exactly to their counterparts in i havebeen given the same reference numerals.

In Fig. 2, the output potential of the preamplier 2i! is impressedacross a condenser |52 in series with a resistance |54. As long as theoutput potential of the pre-amplifier 20 is conetant, it appearsentirely across the condenser |52, therebeing no current flow throughresistance and no potential drop across it. When the output potential ofpre-amplier 2U changes, a potential drop appears across resistance |54which is a measure of the rate of change of the pre-amplier outputpotential. This potential drop across resistance |54 is amplied by anamplifier |58 so that the entire potential appearing between conductors|50 and |50 is equal to the sum of the potential drop across condenser iplus lthe amplied potential across resistance |54. The potential dropacross condenser i52 is a measure of the temperature at the thermocoupleI4, while the potential drop across resistance |54 is a measure of thedifference between the thermocouple temperature and the exhaust gastemperature. The potential between conductors |50 and i60 is therefore ameasure of the exhaust gas temperature, and may be indicated by avoltmeter |62 and impressed on the Wheatstone bridge circuit 36 in thesame manner as the output potential of amplifier 34 was so impressed inFig. 1. The resistance |54 is manually adjustable so that it may bevaried to correspond with the lag due to the protective casing.A

While I show and describe certain preferred embodiments of my invention,other modifications thereof will readily occur to those skilled in theart, and I therefore intend my invention to be limited only by theappended claims.

I claim as my invention:

1. Control apparatus for an internal combustion engine of the jetpropulsion type, comprising means for controlling the flow of fuel tosaid engine, a temperature responsive electrical device heated by theexhaust gases from said engine through the medium of an interposedthermal circuit and having an electrical characteristic varying inaccordance With temperature but lagging behind temperature changes byreason of the effect of said thermal circuit, means for producing anelectrical potential varying with said characteristic, means forobtaining from said potential two component potentials, one varying withthe temperature at said device and the other varying with the rate ofchange of said temperature, means for amplifying a preselectedproportion of said two components to compensate the output of saidamplifying means for the lag produced by the thermal circuit of saiddevice so that said output accurately measures the exhaust gastemperature, and means responsive to said output for operating said fuelflow controlling means, said last named means being effective When saidtemperature exceeds a predetermined value to reduce the ow of fuel tosaid engine.

2. Control apparatus for an internal combustion engine of the jetpropulsion type, comprising means for controlling the flow of fuel tosaid engine, a temperature responsive electrical device heated by theexhaust gases from said engine through the medium of an interposedthermal circuit and having an electrical characteristic varying inaccordance with temperature but lagging behind temperature changes byreason of the effect of said thermal circuit, means for producing anelectrical potential varying with said characteristic, an electricalresistance element, an electrical reactance element, means forimpressing said potential across said elements in series so that thepotential drop across one of said elements varies with the temperatureat said device and the potential drop across the other of said elementsvaries with the rate of change of said temperature, means for amplifyingthe potential drop across said other element to compensate for the lagproduced by the thermal circuit of said device so that the sum of thepotential drop across said one element and the output of said amplifyingmeans accurately measures the exhaust gas temperature, and meansresponsive to said sum for operating said fuel iiow controlling means,said last named means being effective when said temperature exceeds apredetermined value to reduce the ow of fuel to said engine.

3. Control apparatus for an internal combustion engine of the jetpropulsion. type, comprising means for controlling the ow of fuel tosaid engine, a temperature responsive electrical device heated by theexhaust gases from said engine through the medium of an interposedthermal circuit and having an electrical characteristic varying inaccordance with temperature but lagging behind temperature changes byreason of the effect of said thermal circuit, means for producing anelectrical potential varying with said characteristic, an electricalresistance element, an electrical reactance element, means forimpressing said potential across said elements in series so that thepotential drop across one of said elements varies with the temperatureat said device and the potential drop across the other of said elementsvaries with the rate of change of said temperature, means for amplifyingthe potential drop across said other element and a portion only of thepotential drop across said one element to compensate the output of saidamplifying means for the lag produced by the thermal circuit of saiddevice so that said output accurately measures the exhaust gastemperature, and means responsive to said output for operating said fuelow controlling means, said last named means being effective when saidtemperature exceeds a predetermined value to reduce the flow of fuel tosaid engine.

References Cited in the le of this patent UNITED STATES PATENTS NumberName Date 1,312,899 Esnault-Pelterie Aug. 12, 1919 2,054,120 De FlorezSept. 15, 1936 2,095,991 Lysholm Oct. 19, 1937 2,282,726 Jones May 12,1942 2,404,428 Bradbury July 23, 1946 2,413,128 Wills Dec. 24, 1946

